This invention is related to the conversion of hydrocarbon streams. More particularly, it is related to the reforming of hydrocarbon fractions over catalysts containing platinum and rhenium.
The reforming of hydrocarbon streams is one of the important petroleum refining processes that may be employed to provide high-octane-number hydrocarbon blending components for gasoline. In the typical reforming process, the reactions comprise dehydrogenation reactions, isomerization reactions, and hydrocracking reactions. The dehydrogenation reactions include the dehydrogenation of cyclohexanes to aromatics, the dehydroisomerization of alkylcyclopentanes to aromatics, the dehydrogenation of paraffins to olefins, and the dehydrocyclization of paraffins and olefins to aromatics. The isomerization reactions include isomerization of n-paraffins to isoparaffins, the hydroisomerization of olefins to isoparaffins, the isomerization of alkylcyclopentanes to cyclohexanes, and the isomerization of substituted aromatics. The hydrocracking reactions include hydrocracking of paraffins and hydrodesulfurization. Adequate discussions of the reactions occurring in a reforming reaction zone are presented in CATALYSIS, Vol. VI, P. H. Emmett, editor, Reinhold Publishing Corporation, 1958, pages 497-498, and PETROLEUM PROCESSING, R. J. Hengstebeck, McGraw-Hill Book Company, Inc., 1959, pages 179-184.
It is well known by those skilled in the art that several catalysts are capable of reforming naphthas and hydrocarbons that boil in the gasoline boiling range. Although reforming can be carried out through the use of several types of catalysts, namely, molybdena-on-alumina catalysts, chromium-oxides-on-alumina catalysts, platinum-halogen-on-alumina catalysts, platinum-rhenium-halogen-on-alumina catalysts, and platinum-aluminosilicate-material-alumina catalysts, the catalysts employing platinum as a hydrogenation component and rhenium as a promoter are generally employed today in the reforming processes of the petroleum industry.
Kluksdahl, in U.S. Pat. No. 3,415,737, discloses the platinum-rhenium catalyst and its use for the reforming of hydrocarbon fractions. This catalyst has both platinum and rhenium deposited on the same support material. He provides that the sulfur content of the system should be minimal and that the catalyst should be presulfided to prevent run-away temperatures due to excessive hydrocracking.
It is known in the art that a reforming catalyst may contain more than one Group VIII metal, for example, platinum and palladium. In U.S. Pat. No. 3,173,856, Burton, et al., teach reforming with a catalyst comprising platinum and/or palladium on eta-alumina. In U.S. Pat. No. 3,554,901, Kominami, et al., teach the aromatization of hydrocarbons at a temperature of 400.degree. C. to 650.degree. C. with a catalyst that is prepared by impregnating a carrier, such as silica, alumina, or silica-alumina, with a solution containing 0.1 to 1 wt. % platinum, 0.1 to 1 wt.% palladium, and 5 to 25 wt.% chromium oxide, and treating the impregnated material with hydrogen. In U.S. Pat. No. 3,694,348, Bursian, et al., disclose the aromatization of hydrocarbons at a temperature of 400.degree. C. to 550.degree. C. and a pressure of up to 20 atmospheres over platinum-on-alumina catalyst containing 0.1 to 5 wt.% palladium and 0.1 to 5 wt.% of at least one element from the scandium subgroup of Group III of the Periodic Table of Elements and/or the zirconium subgroup of Group IV. In Example 5 of this latter patent, there is employed a catalyst containing 0.6 wt.% platinum and 0.2 wt.% palladium on alumina.
In U.S. Pat. No. 4,124,490, Collins, et. al., teach reforming that employs a catalyst comprising a support, at least one platinum-group metal component, and at least one rhenium component at two different temperature levels.
In U.S. Pat. No. 4,124,491, Antos, et al., disclose reforming with a selectively sulfided acidic multi-metallic catalyst comprising one or more Group VIII metals, a sulfided rhenium component, a halogen component, and a Ziegler alumina. The patent teaches that the catalyst may contain platinum, iridium, rhodium, or palladium; platinum and iridium; and platinum and rhodium.
The use of mechanical mixtures of components for catalysts is well known. Kittrell, in U.S. Pat. No. 3,535,231, considers a process for the conversion of distillates and solvent-deasphalted residua employing a catalyst consisting of a physical mixture of particles of a first catalyst comprising a layered clay-type crystalline aluminosilicate material and a component selected from rhenium and compounds of rhenium and a second catalyst comprising a layered clay-type crystalline aluminosilicate material, a component selected from Group VIII metals and compounds thereof, and a component selected from a silica-alumina gel, silica-alumina-titania gel, and silica-alumina-zirconia gel. Hydrocracking, hydrodesulfurization, hydrodenitrification, hydrogenation, and hydroisomerization processes are included.
Thorn, et al., in U.S. Pat. No. 2,890,178, disclose a method for preparing a reforming catalyst, wherein an intermediate catalytic concentrate is prepared by impregnating a finely-divided carrier with about 1 to about 35 wt.% of a platinum group metal compound, the intermediate concentrate is dried and a major proportion of a finely-divided, predried, adsorptive metal oxide containing a major proportion of alumina and which is free of platinum group metal is mixed with a minor proportion of the concentrate particles.
Sinfelt, et al., in U.S. Pat. No. 3,346,510, disclose a bifunctional catalyst wherein hydrogenation-dehydrogenation metal has been impregnated on a non-acidic component that has been physically mixed with separate particles comprising an acidic component, for example, a catalyst composed of platinum on alumina physically admixed with particles of hydrogen-form Y-type crystalline aluminosilicate material.
Prater, et al., in U.S. Pat. No. 2,854,404, consider a reforming catalyst that consists essentially of a mechanical mixture of finely-divided particles of a porous inert carrier having deposited thereon a small amount of one or more of the platinum group metals and finely-divided particles of porous eta-alumina having incorporated therein an activating amount of halogen. They consider activated alumina derived from alpha-alumina trihydrate particles which are less than 100 microns in diameter to be a preferred porous inert carrier.
Schwarzenbek, in U.S. Pat. No. 2,897,137, discloses a reforming catalyst comprising a catalyst containing about 1 to about 25 wt.% of platinum supported on a carrier material in physical admixture with a carrier material in an amount sufficient to provide an average platinum concentration of about 0.05 to about 0.95 wt.% in the total mixture. An example is a mixture of alumina and platinum-on-alumina.
Hass, et al., in U.S. Pat. No. 3,619,127, consider a catalyst that can be used for treating automobile exhaust gases, which catalyst comprises a mechanical mixture of discrete particles, part of which contains platinum metal supported on a suitable support and part of which contains Group VI metal oxides supported on the same or a different support. Supports of alumina and silica-alumina are mentioned.
Sinfelt, et. al., in U.S. Pat. No. 3,925,196, disclose a reforming catalyst that comprises alumina and an alumina-supported multi-metallic component comprising one or more Group VIII metals alone or in combination with Group VIIB and/or Group IB metals. In U.S. Pat. No. 3,789,020, the same patentees indicate that the metals are supported on less than about one quarter of the total refractory material to form the supported component and the supported component is admixed with the remaining refractory material. Examples of refractory material are alumina, silicaalumina, crystalline aluminosilicate material, silicamagnesia, and mixtures thereof.
In German Offenlegungsschrift No. P 26 27 822, Roberts, et al., disclose a reforming catalyst consisting of a mechanical mixture of particles of platinum on a first solid support and particles of a rhenium-containing component on a second solid support and a process for reforming heavy gasoline, which process employs such catalyst. They do not provide any restriction or limitation that is directed to particle size or particle size distribution. They do indicate that the platinum-containing particles can also contain one or more catalytic components, such as palladium, iridium, rhodium, gallium, germanium, or tin, or compounds thereof.
There has now been found an improved catalyst for the reforming of petroleum hydrocarbon streams and a reforming process that employs such improved catalyst.